Fuel supply system for an internal combustion engine with a hybrid-drive fuel pump

ABSTRACT

A fuel supply system for internal combustion engines has a fuel pump that can be driven both by an electric drive and by the engine. The result is good starting performance of the engine and low demand for driving power on the part of the fuel pump during operation of the engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. 371 application of PCT/DE 00/04368,filed on Aug. 12, 2000.

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The invention is based on a fuel supply system for internal combustionengines, having an electrically driven fuel pump, in which the intakeside of the fuel pump in fluid communication with a fuel tank, and thecompression side of the fuel pump in fluid communication with theengine.

2. Description Of The Prior Art

In a known fuel supply system, an electrically driven fuel pump pumpsthe fuel from the fuel tank to the engine. The electric drive of thefuel pump must be designed for the entire operating life of the engine.This means that upon engine starting if the battery is weak or it isvery cold outside, the pumping capacity of the fuel pump is reducedmarkedly, since the voltage in the on-board electrical system drops toabout 50% of the rated voltage. Consequently the fuel supply to theengine and thus the starting performance of the engine are not optimal.Furthermore, since the known electric drives are not regulated, thepumping flow of the fuel pump is always the same as the maximum fuelflow required. In idling or at partial load, the excess fuel is returnedto the fuel tank via a return line. This means an unnecessarily highconsumption of electrical energy for driving the fuel pump. Finally, theelectric drive and the fuel pump become unnecessarily expensive.

It is also known to couple a fuel pump directly to the engine and todrive it by the engine. The advantage of this drive concept is due tothe fact that the pumping capacity of the fuel pump is approximatelyproportional to the engine rpm and thus also approximately proportionalto the fuel consumption of the engine. Thus the fuel flow that isreturned to the tank via a return line, and the drive power required forthe fuel pump, are reduced markedly also. A disadvantage of this driveconcept, however, is that upon starting of the engine, the fuel pumpfurnishes only a very slight pumping flow, so that it requires severalrevolutions of the crankshaft of the engine to reach the requisitepressure buildup, for instance, in the fuel injection system of theengine. The result is poor starting performance. Another disadvantage ofthis system is that if the tank is empty, or the first time the tank isfilled at the factory, the engine starter must be actuated for a longtime to attain the requisite fuel pumping. This puts heavy loads on boththe battery and the starter.

OBJECTS AND SUMMARY OF THE INVENTION

The primary object of the invention is to furnish a fuel supply systemwith an improved operating performance compared to the prior art.

According to the invention, this object is attained by a fuel supplysystem for internal combustion engines, having an electrically drivenfuel pump, in which the intake side of the fuel pump is in the fluidcommunication with a fuel tank, in which the compression side of thefuel pump is in the fluid communication with the engine, and in whichthe fuel pump is alternatively driven by the engine.

As a result of the hybrid drive of the fuel pump, the advantages of bothdrive systems can be exploited without doing so at the cost of theirdisadvantages. Upon starting of the engine, the fuel pump is drivenelectrically, so that despite a low crankshaft rpm of the engine, anadequate pumping flow is achieved, and thus the engine is supplied withfuel sufficiently quickly. The result is both good starting performanceand a low load on the starter battery and the starter. These advantagesalso pertain the first time the fuel tank is filled at the factory, orif the fuel tank has been empty.

As soon as the engine is running at a sufficiently high rpm, the driveof the fuel pump is taken over by the engine. As a result, the fuel pumprpm is coupled directly to the engine rpm. An improved match between thepumping flow of the fuel pump and the fuel consumption of the engine isthus attained. This meets the need for fuel pumping suitable for demand.It moreover avoids returning large portions of the fuel pumping flow tothe fuel tank via a return line. As a result of the direct drive of thefuel pump, the efficiency is also increased, since there is no need toconvert the driving power via the generator and the electric drive.

In a further feature of the invention, it is provided that the electricdrive of the fuel pump is a brushless electric motor, so that as soon asthis drive is switched to be currentless, and the fuel pump is driven bythe engine, it can run along with the engine without a significant powerloss. The result is an especially simple, economical design of the fuelsupply system of the invention. Furthermore in this embodiment,especially quiet operation is achieved when the fuel pump is driven bythe engine.

In a variant of the invention, it is provided that the electric drivewill still function at half the rated voltage of the on-board electricalsystem, so that even if the starter battery is weak or its capacity isreduced because of low temperatures, an adequate pumping capacity of thefuel pump is still attained. This design is unobjectionable from thestandpoint that the fuel pump is electrically driven only during thestarting events, and not during the entire operating time of the engine.As a result, the operating time is reduced to a fraction of that of theengine, so that even in brief operation of the electric drive at therated voltage of the on-board electrical system, no overload ensues.

In further variants of the invention, it is provided that a freewheel isdisposed between the electric drive and the fuel pump, and that a secondfreewheel is disposed between the engine and the fuel pump, so that thefuel pump is driven either by the electric drive or by the engine, and areversal of the power flow, for instance from the fuel pump to theengine or from the fuel pump to the electric drive, cannot occur. Thisenhances the operating reliability and minimizes the energy demand forthe fuel pump.

Further features of the invention provided that the drive of the fuelpump is effected on the engine side by the camshaft, the crankshaft, atoothed belt, a V-belt, a control chain, the drive for the water pump orfor the generator, or the high-pressure fuel pump of a fuel injectionsystem, so that an optimal adaptation of the pumping quantity of thefuel pump becomes possible. For instance, the camshaft rotates at onlyhalf the rpm of the crankshaft, so that depending on which shaft thefuel pump is driven by, the rpm differs by the factor of 2. The rpmratio between the engine and the fuel pump can be selected as virtuallyfixed by driving the fuel pump via a toothed belt, V-belt or controlchain. Another criterion for the choice of the drive of the fuel pump interms of the engine can be the structural conditions existing in theregion of the engine, or making assembly as simple as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and advantageous features of the invention will becomeapparent from the description contained below, taken with the singleFIGURE of the drawing which schematically shows the fuel system of theinvention along with an internal combustion engine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A fuel pump 1 communicates on its intake side 3 with a fuel tank 5 via afirst low-pressure fuel line 7. The compression side 9 of the fuel pump1 is in fluid communication via a second low-pressure fuel line 11 witha fuel injection pump 13 of an internal combustion engine 15. Excessfuel pumped to the engine 15 by the fuel pump 1 is returned to the fueltank 5 again via a return line 17. Pump 1 may be a known roller cellpump or a gear pump, for example.

The fuel pump 1 is alternatively driven by an electric drive 19 or apower takeoff shaft 21 of the injection pump 13. Between the electricdrive 19 and the fuel pump 1, a first freewheel 23 is provided. Betweenthe engine 15, or the power takeoff shaft 21 of the injection pump 13,and the fuel pump 1, a second freewheel 25 is provided. By means of thefreewheels 23 and 25, the fuel pump 1 is prevented from being drivensimultaneously by both the engine 15 and the electric drive 19.Moreover, a reversal of the power flow from the fuel pump 1 to theengine 15, or from the fuel pump 1 to the electric drive 19, isprevented.

The electric drive 19 is triggered upon initiating starting of theengine 15. As a result, the pumping flow of the fuel pump 1 isindependent of the rpm of the engine 15, so that the engine is quicklysupplied with sufficient fuel. This is especially important if the tankhas run empty or when the tank is filled for the first time at thefactory.

As soon as the engine 15 is running at a high enough rpm, the electricdrive 19 is switched to be currentless, and the fuel pump 1 is driven bythe engine 15. As a result, a pumping flow of the fuel pump 1 thatcorresponds to the fuel consumption of the engine 15 is attained, sothat only little fuel has to be returned to the tank 5 by the engine 15or the fuel injection pump 13 via the fuel return line 17. Hence thefuel supply system of the invention leads to very good startingperformance of the engine 15, even under difficult conditions, and to areduction in the driving power demand of the fuel pump 1 during theoperation of the engine 15, so that the fuel consumption of the engine15 is reduced accordingly.

Because the operating time of the electric drive is reduced markedlycompared to that of the engine, the electric drive can be designed suchthat it is still functional even at only about half the rated voltage ofthe on-board electrical system. As a result, even if the starter batteryis weak or its capacity is reduced because of low temperatures, anadequate pumping capacity of the fuel pump is still attained.

The drive in terms of the engine of the fuel pump 1 by a power takeoffshaft 21 of the fuel injection pump 13 is only one possible driveoption, among many. The drive of the fuel pump 1 in terms of the enginecan also be done by the camshaft, the crankshaft, a toothed belt, aV-belt, a control chain, or by the drive of the water pump or of thegenerator. An optimal adaptation of the pumping quantity of the fuelpump, or the given structural conditions in the region of the engine,and simplification of assembly can be attained by the suitable choice ofthe drive in terms of the engine.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A fuel supply system for an internal combustionengine (15), comprising an electrically driven fuel pump (1) having anintake side (3) connected in fluid communication with a fuel tank (5), acompression side (9) connected in fluid communication with the engine(15), and, means (21,25) for alternatively driving the fuel pump (1) bythe engine (15).
 2. The fuel supply system of claim 1 wherein theelectric drive (19) of the fuel pump (1) is a brushless electric motor.3. The fuel supply system of claim 1 wherein the electric drive (19) isstill functional at half the rated voltage of the on-board electricalsystem.
 4. The fuel supply system of claim 2 wherein the electric drive(19) is still functional at half the rated voltage of the on-boardelectrical system.
 5. The fuel supply system of claim 1 furthercomprising a first freewheel (23) disposed between the electric drive(19) and the fuel pump (1).
 6. The fuel supply system of claim 2 furthercomprising a first freewheel (23) disposed between the electric drive(19) and the fuel pump (1).
 7. The fuel supply system of claim 3 furthercomprising a first freewheel (23) disposed between the electric drive(19) and the fuel pump (1).
 8. The fuel supply system of claim 1 furthercomprising a second freewheel (25) disposed between the engine (15) andthe fuel pump (1).
 9. The fuel supply system of claim 2 furthercomprising a second freewheel (25) disposed between the engine (15) andthe fuel pump (1).
 10. The fuel supply system of claim 3 furthercomprising a second freewheel (25) disposed between the engine (15) andthe fuel pump (1).
 11. The fuel supply system of claim 5 furthercomprising a second freewheel (25) disposed between the engine (15) andthe fuel pump (1).
 12. The fuel supply system of claim 1 wherein thedrive of the fuel pump (1) is effected on the engine side by the enginecamshaft, the crankshaft, a toothed belt, a V-belt, the drive for thewater pump or for the generator, or the high-pressure fuel pump (13) ofa fuel injection system.
 13. The fuel supply system of claim 2 whereinthe drive of the fuel pump (1) is effected on the engine side by theengine camshaft, the crankshaft, a toothed belt, a V-belt, the drive forthe water pump or for the generator, or the high-pressure fuel pump (13)of a fuel injection system.
 14. The fuel supply system of claim 3wherein the drive of the fuel pump (1) is effected on the engine side bythe engine camshaft, the crankshaft, a toothed belt, a V-belt, the drivefor the water pump or for the generator, or the high-pressure fuel pump(13) of a fuel injection system.
 15. The fuel supply system of claim 5wherein the drive of the fuel pump (1) is effected on the engine side bythe engine camshaft, the crankshaft, a toothed belt, a V-belt, the drivefor the water pump or for the generator, or the high-pressure fuel pump(13) of a fuel injection system.
 16. The fuel supply system a claim 8wherein the drive of the fuel pump (1) is effected on the engine side bythe engine camshaft, the crankshaft, a toothed belt, a V-belt, the drivefor the water pump or for the generator, or the high-pressure fuel pump(13) of a fuel injection system.
 17. The fuel supply system of claim 1wherein the fuel pump (1) is a roller cell pump or a geared pump. 18.The fuel supply system of claim 2 wherein the fuel pump (1) is a rollercell pump or a geared pump.
 19. The fuel supply system of claim 3wherein the fuel pump (1) is a roller cell pump or a geared pump. 20.The fuel supply system of claim 5 wherein the fuel pump (1) is a rollercell pump or a geared pump.